Conventionally, in the field of semiconductor fabrication and so on, a polymer having enhanced solubility to a developing solution due to its main chain cut by irradiation of ionizing radiation such as electron beams or short wavelength light such as ultraviolet rays (hereinafter, the ionizing radiation and the short wavelength light may be collectively referred to as “ionizing radiation”) is used as positive resist of a main chain scission type.
For example, PTL 1 set forth below discloses, as positive resist of the main chain scission type having high sensitivity, positive resist formed of α-alkylstyrene α-chloroacrylate copolymer containing 30 mol % to 70 mol % of an α-methylstyrene unit and 30 mol % to 70 mol % of a methyl α-chloroacrylate unit.
Also, for example, PTL 2 set forth below discloses an α-alkylstyrene α-chloroacrylate copolymer, usable as positive resist having high resolution, having weight-average molecular weight of 9500 to 35000 and molecular weight distribution (weight-average molecular weight/number-average molecular weight) of 1.05 to 1.25. The PTL 2 prepares the α-alkylstyrene α-chloroacrylate copolymer having the above property by solution polymerization using dioxane as a polymerization solvent.